Scientists are continuing to test dead birds near the Fife village in which one swan with the H5N1 avian flu virus was found last week.

Since the dead swan in Cellardyke was confirmed as having the virus, there has been a marked increase in the number of dead birds being reported.

But every other bird analysed so far in Scotland has tested negative.

Scotland's eight laboratories that can test for bird flu have remained open this weekend and will open at Easter.

Out of nearly 2,500 calls from across the UK to a hotline on Friday, no suspected bird flu cases have been identified, according to the Department for the Environment Food and Rural Affairs.

A spokeswoman said so far no so-called "report" cases - which are suspected to be bird flu and are prioritised for testing - had been identified.

"Every case that has been tested has come back negative," she added.

Head of veterinary operations Derick McIntosh said everything possible was being done to stop the virus spreading.

Scottish Executive regional operations director Paul Neison said an extra 70 staff had been drafted in to the surveillance and protection zones around the coastal village of Cellardyke, where the swan was discovered.

A six-mile (10km) surveillance zone and 1.8 mile (3km) protection zone in place around the area will remain for at least 30 days from the day the swan was found.

The Scottish Executive has also declared a wild bird risk area of 965 square miles (2,500km) - stretching from Fife to Aberdeenshire - which includes 175 registered poultry premises, containing 3.1 million birds.

About 48 - housing 260,000 birds - are free-range premises.

In this area captive birds must be housed where possible, or at least isolated to minimise contact with wild birds. Gatherings of poultry or other captive birds is banned.

Mr McIntosh said scientists had already seen the number of samples being sent for testing increase "substantially" since the UK's first H5N1 case was confirmed.

Experts were out in the field this weekend collecting carcasses, photographing them for identification and sending samples for testing, said Mr McIntosh.

Some lab staff were working 12 to 14 hour shifts to keep up with the workload, he said.